Make the black tiles out of that black material that absorbs all light and swim over the void.

Fun fact about Vantablack- Because it absorbs all light, it heats up very fast. If exposed to direct sunlight, it takes in all the UV and heat and contains them, and can reach heats well over 212°F, the boiling point of water. So if you did coat the pool in that material, the water would boil as soon as the sun touched it, killing everyone swimming in it.

But that’s not all. The flash boiling of an entire pool of chlorinated water would release the chlorine as gas, which would kill everyone within a 200ft radius of the pool. And it doesn’t end there.

The release of chlorine gas combined with the heat of the black tiles would be more than sufficient to fuse the boiled hydrogen ions with the chlorine, creating an explosive reaction with the nitrogen in the air. So shortly after everyone in the pool boils and everyone around the pool dies of chlorine gas poisoning, the region would explode with the force of a small atomic bomb (8kt for a pool like those pictured above), leveling about 50 city blocks.

You’d think that would be bad enough, but get this-

Such chemical explosions expel gamma rays. Gamma rays ionize hematite, which is the mineral from which the black material mentioned is made. This creates Scopohyoscpnol, a compound known as “The Zombie Drug” because it essentially erases the brain and induces cannibalistic tendencies in its victim. It can be transmitted through saliva, infecting all who are bitten within hours.

So basically, if you did have Vantablack tiles in your pool, you would boil your friends, poison your neighbors, nuke your city, and condemn the globe to a zombie plague. But to be fair, it would look pretty cool.